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Borrowings - Additional Information (Detail) - Commercial Credit Agreement - USD ($)
Nov. 19, 2013
May. 31, 2015
May. 31, 2014
Line of Credit Facility [Line Items]      
Maximum aggregate outstanding principal amount under Commercial Credit Agreement $ 50,000,000    
Borrowing outstanding   $ 2,387,000 $ 0
Weighted average interest rate     1.25%
JP Morgan Chase Bank [Member]      
Line of Credit Facility [Line Items]      
Maximum aggregate outstanding principal amount under Commercial Credit Agreement $ 25,000,000    
Line of Credit Facility, Expiration Period 3 years    
Line of Credit Facility, Additional Borrowing Capacity $ 25,000,000    
JP Morgan Chase Bank [Member] | Eurodollar [Member]      
Line of Credit Facility [Line Items]      
Debt Instrument, Basis Spread on Variable Rate 0.75%    
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage 0.10%    
JP Morgan Chase Bank [Member] | Base Rate [Member]      
Line of Credit Facility [Line Items]      
Debt Instrument, Basis Spread on Variable Rate 2.50%    
JP Morgan Chase Bank [Member] | London Interbank Offered Rate (LIBOR) [Member]      
Line of Credit Facility [Line Items]      
Debt Instrument, Basis Spread on Variable Rate 2.00%    
Maximum | JP Morgan Chase Bank [Member] | Eurodollar [Member]      
Line of Credit Facility [Line Items]      
Line of Credit Facility, Unused Capacity, Commitment Fee Threshold $ 8,000,000